JP2007250439A - Hydrogen storage alloy for alkaline storage battery, and alkaline storage battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enhance corrosion resistance and improve a cycle life of an alkaline storage battery in a state that hydrogen storing capacity in a hydrogen storage alloy for the alkaline storage battery is maintained high. <P>SOLUTION: For a negative electrode 2 of the alkaline storage battery, a hydrogen storage alloy is used which is expressed by a general formula Ln<SB>1-x</SB>Mg<SB>x</SB>Ni<SB>y-a-b</SB>Al<SB>a</SB>M<SB>b</SB>(in the formula, Ln is at least one kind of element selected from rare earth elements containing Y, M is at least one kind of element selected from V, Nb, Ta, Cr, Mo, Mn, Fe, Co, Ga, Zn, Sn, In, Cu, Si, P, B, Zr, and Ti, and conditions of 0.05≤x≤0.35, 2.8≤y≤3.9, 0.05≤a≤0.30, 0≤b≤0.5 is satisfied), and in which a half value width Δθ<SB>1</SB>of the strongest peak appearing in a range of 2θ=44 to 46° is smaller than the half value width Δθ<SB>2</SB>of the strongest peak appearing in the range of 2θ=34.5 to 36.5° in an X-ray diffraction measurement using Cu-Kα ray as the X-ray. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an alkaline storage battery including a positive electrode, a negative electrode using a hydrogen storage alloy, and an alkaline electrolyte, and a hydrogen storage alloy for an alkaline storage battery used for the negative electrode of the alkaline storage battery. It is characterized in that the corrosion resistance is enhanced and the cycle life of the alkaline storage battery is improved while maintaining a high hydrogen storage capacity in the hydrogen storage alloy for the alkaline storage battery to be used.

  Conventionally, nickel-cadmium storage batteries have been widely used as alkaline storage batteries, but in recent years they have a higher capacity than nickel-cadmium storage batteries and are superior in environmental safety because they do not use cadmium. Therefore, nickel-hydrogen storage batteries using a hydrogen storage alloy for the negative electrode have come to attract attention.

  And the alkaline storage battery which consists of such a nickel-hydrogen storage battery comes to be used for various portable apparatuses, and it is anticipated that this alkaline storage battery will be further improved in performance.

Here, in such an alkaline storage battery, the hydrogen storage alloy used for the negative electrode generally includes a rare earth-nickel hydrogen storage alloy whose main phase is a CaCu ₅ type crystal, Ti, Zr, V and Ni. A hydrogen storage alloy or the like whose main phase is a Laves phase AB ₂ type crystal is generally used.

  However, the hydrogen storage alloy as described above does not necessarily have sufficient hydrogen storage capacity, and it has been difficult to further increase the capacity of the alkaline storage battery.

In recent years, in order to improve the hydrogen storage capacity of the rare earth-nickel hydrogen storage alloy, Mg or the like is contained in the rare earth-nickel hydrogen storage alloy, and Ce ₂ Ni other than CaCu ₅ type is used. It has been proposed to use a hydrogen storage alloy having a crystal structure such as ₇ type or CeNi ₃ type (see, for example, Patent Document 1).

However, even in the hydrogen storage alloy in which the rare earth-nickel-based hydrogen storage alloy contains Mg or the like and has a crystal structure such as Ce ₂ Ni ₇ type or CeNi ₃ type, the corrosion resistance is not always sufficient, In the case of an alkaline storage battery using such a hydrogen storage alloy, there is still a problem that a sufficient cycle life cannot be obtained.
JP 2002-69554 A

The present invention relates to an alkaline storage battery using a hydrogen storage alloy for an alkaline storage battery having a crystal structure such as Ce ₂ Ni ₇ type or CeNi ₃ type other than CaCu ₅ type containing rare earth elements, nickel and magnesium as a negative electrode. In a state where the hydrogen storage amount in the hydrogen storage alloy for alkaline storage batteries is maintained high, the corrosion resistance is improved and the cycle life in the alkaline storage battery is improved. It is to be an issue.

In the hydrogen storage alloy for alkaline storage batteries according to the present invention, in order to solve the above-described problems, the general formula Ln _1-x Mg _x Ni _yab Al _a M _b (wherein Ln is selected from rare earth elements including Y). And at least one element selected from the group consisting of V, Nb, Ta, Cr, Mo, Mn, Fe, Co, Ga, Zn, Sn, In, Cu, Si, P, B, Zr, and Ti. It is a seed element and satisfies the following conditions: 0.05 ≦ x ≦ 0.35, 2.8 ≦ y ≦ 3.9, 0.05 ≦ a ≦ 0.30, and 0 ≦ b ≦ 0.5. In the X-ray diffraction measurement using the Cu—Kα ray as an X-ray source, the half-value width Δθ _{1 of the} strongest peak appearing in the range of 2θ = 44 to 46 ° is in the range of 2θ = 34.5 to 36.5 °. It was made to be smaller than the half-value width Δθ _{2 of the} strongest peak appearing in FIG.

Here, the hydrogen storage alloy for alkaline storage battery has a long-period structure in which CaCu ₅ type lattice and Laves type AB ₂ lattice are regularly arranged in the c-axis direction, and Ce ₂ Ni ₇ type (P63 / mmc). Or a similar crystal structure, such as Gd ₂ Ni ₇ type (R-3m), PuNi ₃ type (R-3m), CeNi ₃ type (P63 / mmc), Ce ₅ Co ₁₉ type (R-3m), Pr ₅ Co ₁₉ type (P63 / mmc) crystal structure.

And in the above-mentioned Ce ₂ Ni ₇ type or a hydrogen storage alloy for alkaline storage batteries having a crystal structure similar to this, the strongest peak appearing in the range of 2θ = 34.5 to 36.5 ° is attributed to the (xy0) plane, The strongest peak appearing in the range of 2θ = 44 to 46 ° is attributed to the (xyz) plane. In addition, the half-value width of these strongest peaks changes due to crystal distortion due to changes in interplanar spacing or the size of the crystallite, and these half-value widths increase as the crystal strain increases. The smaller it becomes, the larger it becomes.

Then, as the half-value width Δθ _{1 of the} strongest peak appearing in the range of 2θ = 44 to 46 ° becomes smaller, the distortion of the crystal in the c-axis direction becomes smaller and the crystallite becomes larger. It is thought that the distortion in the is relieved.

  Further, in the alkaline storage battery of the present invention, in the alkaline storage battery including the positive electrode, the negative electrode using the hydrogen storage alloy, and the alkaline electrolyte, the above-described hydrogen storage alloy for alkaline storage battery is used for the negative electrode. did.

In the hydrogen storage alloy for alkaline storage batteries according to the present invention, the general formula Ln _1-x Mg _x Ni _yab Al _a M _b (wherein Ln is at least one element selected from rare earth elements including Y, M is V , Nb, Ta, Cr, Mo, Mn, Fe, Co, Ga, Zn, Sn, In, Cu, Si, P, B, Zr, and Ti, at least 0.05 ≦ x ≦ 0.35, 2.8 ≦ y ≦ 3.9, 0.05 ≦ a ≦ 0.30, 0 ≦ b ≦ 0.5). In the X-ray diffraction measurement using the source, the half-value width Δθ _{1 of the} strongest peak appearing in the range of 2θ = 44 to 46 ° is more than the half-value width Δθ _{2 of the} strongest peak appearing in the range of 2θ = 34.5 to 36.5 °. As described above, the distortion in the c-axis direction of the crystal is reduced as described above, and the result is The crystallite becomes larger, the strain at the time of occlusion and release of hydrogen is relaxed, and the hydrogen storage alloy for alkaline storage batteries is suppressed from being pulverized.

  As a result, in the alkaline storage battery of the present invention using the hydrogen storage alloy for alkaline storage batteries as described above for the negative electrode, when charged and discharged, the hydrogen storage alloy for alkaline storage batteries is pulverized and the corrosion resistance decreases. Is prevented, and the cycle life of the alkaline storage battery is improved.

  Hereinafter, the hydrogen storage alloy for an alkaline storage battery according to an embodiment of the present invention and the alkaline storage battery using the hydrogen storage alloy for the alkaline storage battery will be described in detail, a comparative example will be given, and the alkaline storage battery according to the embodiment of the present invention will be described. In, it is clarified that the cycle life is improved. In addition, the hydrogen storage alloy for alkaline storage batteries and alkaline storage battery in this invention are not limited to what was shown in the following Example, It can implement by changing suitably in the range which does not change the summary.

Example 1
In Example 1, in producing a hydrogen storage alloy for an alkaline storage battery used for a negative electrode, rare earth elements La, Pr, and Nd, Mg, Ni, and Al are mixed so as to have a predetermined alloy composition, This was melted at 1500 ° C. in a high-frequency induction melting furnace in an argon gas atmosphere, and then cooled to obtain a hydrogen storage alloy ingot. As a result of analyzing the composition of the hydrogen storage alloy by high frequency plasma spectroscopy (ICP), the composition of the hydrogen storage alloy was La _0.17 Pr _0.33 Nd _0.33 Mg _0.17 Ni _3.10 Al _0.20 .

  The hydrogen storage alloy ingot was heat treated in an argon atmosphere at a temperature 60 ° C. lower than the liquefaction start temperature for 10 hours to homogenize, and then the hydrogen storage alloy ingot was mechanically pulverized in an inert atmosphere. This was classified to obtain a hydrogen storage alloy powder of Example 1 having the above composition. As a result of measuring the particle size distribution of the hydrogen storage alloy powder using a laser diffraction / scattering particle size distribution measuring device, the average particle size at a weight integral of 50% was 65 μm.

  In preparing the negative electrode, 0.4 parts by weight of sodium polyacrylate, 0.1 part by weight of carboxymethylcellulose, and polytetrafluoroethylene dispersion (100 parts by weight of the above-mentioned hydrogen storage alloy powder) Dispersion medium: water, solid content 60 wt%) was mixed at a ratio of 2.5 parts by weight to prepare a paste. And this paste is uniformly applied to both sides of a conductive core made of a punching metal having a thickness of 60 μm with nickel plating, dried and pressed, and then cut into predetermined dimensions, A negative electrode composed of a hydrogen storage alloy electrode was produced.

  On the other hand, in preparing the positive electrode, nickel hydroxide powder containing 2.5% by weight of zinc and 1.0% by weight of cobalt was put into a cobalt sulfate aqueous solution, and 1 mol of hydroxide was stirred while stirring the powder. A sodium aqueous solution is gradually added dropwise to cause the reaction to a pH of 11, and then the precipitate is filtered, washed with water and dried under vacuum to obtain nickel hydroxide having a surface coated with 5% by weight of cobalt hydroxide. Obtained. Next, the nickel hydroxide thus coated with cobalt hydroxide was impregnated with a 25 wt% aqueous sodium hydroxide solution in a weight ratio of 1:10, and this was stirred at 85 ° C. while stirring for 8 hours. After heat-treating, this was washed with water and dried to obtain a positive electrode material in which the surface of the nickel hydroxide was coated with sodium-containing cobalt oxide. In addition, the valence of cobalt in said cobalt oxide was 3.05.

Subsequently, 95 parts by weight of the positive electrode material, 3 parts by weight of zinc oxide, and 2 parts by weight of cobalt hydroxide were mixed with 50 parts by weight of a 0.2% by weight hydroxypropylcellulose aqueous solution. Were mixed to prepare a slurry. Then, the slurry was filled in a nickel foam having a basis weight of about 600 g / m ² , dried and pressed, and then cut into a predetermined size to produce a positive electrode composed of a non-sintered nickel electrode. .

Then, a nonwoven fabric made of polypropylene is used as a separator, and KOH, NaOH, and LiOH.H ₂ O are included as an alkaline electrolyte in a weight ratio of 8: 0.5: 1, and the total of these is 30% by weight. Using the alkaline electrolyte thus obtained, an alkaline storage battery having a cylindrical shape and a design capacity of 1500 mAh as shown in FIG. 1 was produced.

  Here, in producing the alkaline storage battery, as shown in FIG. 1, a separator 3 is interposed between the positive electrode 1 and the negative electrode 2, and these are spirally wound and accommodated in a battery can 4. The positive electrode 1 is connected to the positive electrode lid 6 via the positive electrode lead 5, and the negative electrode 2 is connected to the battery can 4 via the negative electrode lead 7, and an alkaline electrolyte is injected into the battery can 4. The battery can 4 and the positive electrode lid 6 were sealed via an insulating packing 8, and the battery can 4 and the positive electrode lid 6 were electrically separated by the insulating packing 8. Further, a closing plate 11 urged by a coil spring 10 is provided between the positive electrode cover 6 and the positive electrode external terminal 9 so as to close the gas discharge port 6a provided in the positive electrode cover 6, and the battery When the internal pressure of the battery rises abnormally, the coil spring 10 is compressed so that the gas inside the battery is released into the atmosphere.

(Examples 2-9)
In Examples 2 to 9, in producing a hydrogen storage alloy for an alkaline storage battery, the ratio of mixing rare earth elements La, Pr and Nd, Mg, Ni and Al in the case of Example 1 above The alkaline storage batteries of Examples 2 to 9 were used in the same manner as in Example 1 except that the hydrogen storage alloy powder having the composition shown in Table 1 below was used. Was made.

(Comparative Examples 1 and 2)
Also in Comparative Examples 1 and 2, in producing the hydrogen storage alloy for alkaline storage batteries, the ratio of mixing rare earth elements La, Pr and Nd, Mg, Ni and Al in the case of Example 1 above. The alkaline storage batteries of Comparative Examples 1 and 2 were used in the same manner as in Example 1 except that the hydrogen storage alloy powder having the composition shown in Table 1 below was used. Was made.

Here, the hydrogen storage alloy powders prepared in Examples 1 to 9 and Comparative Examples 1 and 2 were further pulverized for 10 minutes using a pulverizer (Type A10S2 manufactured by IKA Labortechnik). For each hydrogen storage alloy powder crushed into an X-ray diffraction measurement apparatus (XD-610, manufactured by Shimadzu Corporation) using Cu-Kα ray as an X-ray source, tube voltage 40 kV, tube current 40 mA, scan speed 0 X-ray diffraction measurement was performed under the conditions of 0.5 ° / min and a light receiving slit width of 0.3 mm, and the half-value width Δθ ₁ (° of the strongest peak appearing in the range of 2θ = 44 to 46 ° based on the obtained peak profile. ) And 2θ = 34.5-36.5 °, the half-value width Δθ ₂ (°) of the strongest peak was calculated, and the results are shown in Table 1.

As a result, in the hydrogen storage alloys prepared in Examples 1 to 9, the half-value width Δθ _{1 of the} strongest peak appearing in the range of 2θ = 44 to 46 ° is in the range of 2θ = 34.5 to 36.5 °. Whereas the full width at half maximum Δθ _{2 of the} strongest peak appeared was smaller than that of the hydrogen storage alloys produced in Comparative Examples 1 and 2, the full width at half maximum Δθ _{1 of the} strongest peak that appeared in the range of 2θ = 44 to 46 ° was It was larger than the half-value width Δθ _{2 of the} strongest peak appearing in the range of 2θ = 34.5 to 36.5 °.

  Next, the alkaline storage batteries of Examples 1 to 9 and Comparative Examples 1 and 2 prepared as described above were left in a temperature atmosphere of 45 ° C. for 10 hours, and then each alkaline storage battery was subjected to 16 mA at a current of 150 mA. After charging for a period of time, the battery was discharged at a current of 1500 mA until the battery voltage reached 1.0 V, and this was regarded as one cycle, and charging / discharging for 3 cycles was performed.

  Then, the alkaline storage batteries of Examples 1 to 9 and Comparative Examples 1 and 2 that were charged and discharged for 3 cycles as described above were disassembled, and the hydrogen storage alloy particles were taken out from the respective negative electrodes, and this was washed with water. After drying under reduced pressure, the oxygen concentration in each hydrogen storage alloy was measured using an oxygen analyzer (RO-416DR manufactured by Leco). Then, the oxygen concentration in each of the hydrogen storage alloys of Examples 2 to 9 and Comparative Examples 1 and 2 was calculated using the oxygen concentration in the hydrogen storage alloy of Example 1 as the reference 100, and the results are shown in Table 2 below. It was shown to.

As a result, a hydrogen storage alloy is used in which the half width Δθ _{1 of the} strongest peak appearing in the range of 2θ = 44 to 46 ° is smaller than the half width Δθ _{2 of the} strongest peak appearing in the range of 2θ = 34.5 to 36.5 °. In Examples 1 to 9, the full width at half maximum Δθ _{1 of the} strongest peak appearing in the range of 2θ = 44 ° to 46 ° is half width Δθ ₁ of the strongest peak appearing in the range of 2θ = 34.5 to 36.5 °. Compared with those of Comparative Examples 1 and 2 using a hydrogen storage alloy larger than ₂ , the oxygen concentration in the hydrogen storage alloy after charge and discharge was low, and the corrosion resistance of the hydrogen storage alloy was improved.

  And in each alkaline storage battery of Examples 1-9 in this way, as a result of the oxygen concentration in the hydrogen storage alloy after charging / discharging becoming low and improving the corrosion resistance of the hydrogen storage alloy, each of Comparative Examples 1 and 2 Compared with alkaline storage batteries, the cycle life is improved.

It is a schematic sectional drawing of the alkaline storage battery produced in Examples 1-9 and Comparative Examples 1 and 2 of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Positive electrode 2 Negative electrode 3 Separator 4 Battery can 5 Positive electrode lead 6 Positive electrode cover 6a Gas discharge port 7 Negative electrode lead 8 Insulation packing 9 Positive electrode external terminal 10 Coil spring 11 Closure board

Claims (4)

In the general formula _{Ln 1-x Mg x Ni yab} Al a M b ( wherein, at least one element Ln is selected from rare earth elements including Y, M is V, Nb, Ta, Cr, Mo, Mn, Fe , Co, Ga, Zn, Sn, In, Cu, Si, P, B, Zr and Ti, at least one element selected from 0.05 ≦ x ≦ 0.35, 2.8 ≦ y ≦ 3.9, 0.05 ≦ a ≦ 0.30, 0 ≦ b ≦ 0.5), and 2θ = 44 in X-ray diffraction measurement using Cu—Kα rays as an X-ray source. A hydrogen storage alloy for an alkaline battery, wherein the half-value width Δθ ₁ of the strongest peak appearing in the range of ˜46 ° is smaller than the half-value width Δθ _{2 of the} strongest peak appearing in the range of 2θ = 34.5-36.5 ° . 2. The hydrogen storage alloy for alkaline storage batteries according to claim 1, wherein the crystal structure of the alloy is a structure in which CaCu ₅ lattice and Laves AB ₂ lattice are regularly arranged. Occlusion alloy. According to claim 1 or claim 2 for alkaline storage battery hydrogen storage alloy described in, for alkaline batteries hydrogen-absorbing alloy which is a structure in which the crystal structure is similar to this or Ce ₂ Ni ₇ type structure of the alloy.   An alkaline storage battery comprising a positive electrode, a negative electrode using a hydrogen storage alloy, and an alkaline electrolyte, wherein the negative electrode is a hydrogen storage alloy for an alkaline storage battery according to any one of claims 1 to 3. An alkaline storage battery characterized by using.

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